1. Field of the Invention
The present invention relates to a switching power supply device using a nonlinear control manner.
2. Description of the Related Art
FIG. 11A to FIG. 11C are all prior art examples of circuit block diagrams and action waveform diagrams of a switching power supply device using a nonlinear control manner, in which FIG. 11A illustrates a switching power supply device using a hysteretic window manner, FIG. 11B illustrates a switching power supply device using a lower limit detection on-time fixed manner, and FIG. 11C illustrates a switching power supply device using an upper limit detection off-time fixed manner. The switching power supply devices illustrated respectively in FIG. 11A to FIG. 11C are all step-down Direct Current (DC)/DC converters, which reduce an input voltage IN to generate a desired output voltage OUT.
Compared with a switching power supply device using a linear control manner (for example, a voltage mode control manner or a current mode control manner), the switching power supply device using the nonlinear control manner has advantages including simple circuit configuration and capability of achieving a high load response characteristic.
On the other hand, the switching power supply device of the nonlinear control manner is configured to use an output ripple voltage (=a ripple component of an output voltage OUT) to drive a comparator, so as to perform switching control on an output transistor. Consequently, in order to accurately detect the output ripple voltage, a large amplitude (peak value) output ripple is required. Conventionally, therefore, an output capacitor (for example conductive polymer-based) of large Equivalent Series Resistance (ESR) has to be used, thereby limiting selection of parts and increasing cost.
Conventionally a so-called ripple injection technique is utilized, in which a ripple component is externally injected in a forced manner into a reference voltage Vref input into a comparator to drive the comparator steadily. Adopting the ripple injection technology allows steady switching control to be performed even if the amplitude of the output ripple voltage becomes very large. Therefore, a multilayer ceramic capacitor of small ESR may be used as an output capacitor.
A related example in the prior art is shown in Patent document 1.